The incident happened at Fallbrook at the north Beltway on the westbound feeder around 11:30 p.m.
The girls were being driven by their father Luis Aguilar, who police said showed signs of being heavily intoxicated.
Deputies said the 31-year-old drove directly into the traffic light pole, and neither child was properly restrained in the back seat.
Heartbreaking and preventable. Bad enough to put yourself and public at risk, but your own defenseless children as well. Another prime example of what alcohol or drugs can do to one who has over indulged and get behind the wheel of the car. Motor vehicle injuries are a leading https://t.co/V8sqWUZgYr— Ed Gonzalez (@SheriffEd_HCSO) June 6, 2020
The 4-year-old was wearing an adult seat belt while the 5-year-old didn't have anything protecting her.
"If you have the responsibility of children, they don't have a voice, they can't say 'Dad don't drive', they can't say 'I need to be on booster', they rely on you," said Sean Teare, with the district attorney's office.
Aguilar has been charged with murder along with intoxicated assault involving a vehicle.
This is the second crash involving a DWI in less than 24 hours that has killed a minor.
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